Dimethoate and fenthion as packing line treatments for tomatoes against Dacus tryoni (Froggatt)

Abstract

Tomatoes were disinfested of Queensland fruit fly (Dacus tryoni) by using dimethoate or fenthion applied as sprays during grading and packing. Concentrations of 400 mg/L of either insecticide applied through a high-volume recirculatory flood system delivering 16 L/min.m2 were used to treat fruit moving at a speed of 0.5 m/min, on conveyor brushes, so that fruit was flooded for 10 s and remained fully wetted for a further 1 min. Treatment efficacies of 100% against 30 000 eggs and 30 000 larvae were obtained. The treatments were equally effective when used in conjunction with post-treatment cooling to 12.5¦C for 1 week. No tainting problems were detected. Residues of dimethoate (also omethoate for selected samples) and fenthion in treated fruit were found to be less than the Australian Maximum Residue Limits for tomatoes at all times; methods for determination of fenthion and omethoate residues are described. These disinfestation treatments have advantages of automation and efficiency compared with previously proven dip treatments.